The present invention relates to a methodology for generating printed color hardcopy. In particular, the present invention is directed to the utilization of redundant color inks with a methodology for identifying which ink combination from a multitude of possible choices is best utilized in rendering a given image.
Using multiple redundant inks is a technique which has been applied to quality black and white prints using inks of various shades of gray. What makes such a technique desirable is that the halftoning scheme that is employed can be made to always select between two adjacent gray levels. In this way, the intensity difference between neighboring pixels in a region of uniform shade is limited to only the small difference of neighboring gray levels. It is this reduction in contrast between pixels that makes the halftone pattern (unwanted texture) difficult to see and thereby improves the image quality. An exemplary approach to this technique can be found in U.S. Pat. No. 6,014,226 to Harrington et al., which is herein incorporated by reference in its entirety for its teaching.
In U.S. Pat. No. 6,014,226 to Harrington et al., a method of multilevel halftoning is described that allows the definition of halftone patterns using more than two gray levels at a time. This feature can be employed to eliminate the texture contours produced when shades formed by a pattern of two levels blends into a shade formed by a single gray level. The method also gives control over the degree to which a given output gray level is used. This can be employed to limit ink coverage when certain levels require more ink to produce than do others. According to the method: initial pixel intensity ranges are obtained; the initial pixel intensity ranges are compared to at least two overlapping threshold arrays; and selection of enhanced pixel intensity levels are determined for halftone cells according to the comparison results of the initial pixel intensity ranges to at least two overlapping threshold arrays wherein the enhanced pixel intensity levels are a function of results from the comparison.
It would be desirable to implement a similar approach to a color system employing additional inks. Unfortunately, unlike a black-to-white gray scale system which is by nature one-dimensional in range, color is itself by nature a three-dimensional system. Therefore, an approach designed for a gray scale system does not generalize well to colors and color space. For example, such a method may be applied to separate individual color components and in so doing the contrast between two magenta values or the contrast between two cyan values is reduced, but there is no control of the contrast between neighboring magenta and cyan values. Thus, such an approach will result in a pixel with dark magenta and dark cyan next to a pixel with light magenta and light cyan. A better and more pleasing solution for the eye would be a dark magenta and light cyan pixel next to a light magenta and dark cyan pixel. This will result in less perceived unwanted texture in the print. This derives from the fundamental response of the eye being more sensitive to luminance information than it is to chrominance information.
Therefore, as discussed above there exists a need for a technique and methodology which will solve the problem of providing a visually acceptable solution to the problem of using multiple or redundant color inks. Thus, it would be desirable to solve this and other deficiencies and disadvantages with an improved methodology.